Port fuel direct injection (PFDI) engines include both port injection and direct injection of fuel and may advantageously utilize each injection mode. For example, at higher engine loads, fuel may be injected into the engine using direct fuel injection for improved engine performance (e.g., by increasing available torque and fuel economy). At lower engine loads and during engine starting, fuel may be injected into the engine using port fuel injection to provide improved fuel vaporization for enhanced mixing and to reduce engine emissions. Further, port fuel injection may provide an improvement in fuel economy over direct injection at lower engine loads. Further still, noise, vibration, and harshness (NVH) may be reduced when operating with port injection of fuel. In addition, both port injectors and direct injectors may be operated together under some conditions to leverage advantages of both types of fuel delivery or in some instances, differing fuels.
In PFDI engines, a lift pump (also termed, low pressure pump) supplies fuel from a fuel tank to both port injectors and a direct injection fuel pump (also termed, high pressure pump). The direct injection fuel pump may supply fuel at a higher pressure to direct injectors. To improve atomization of fuel supplied via port injection, fuel supplied to the port injectors may also be pressurized by a compression chamber of the direct injection fuel pump. As such, the low pressure pump may operate at a lower thermal efficiency (e.g., 1% thermal efficiency) while the high pressure pump may operate at a higher thermal efficiency (e.g., 90% thermal efficiency). Accordingly, the high pressure pump with higher thermal efficiency may be utilized to fuel the port injectors as well as the direct injectors.
The inventors herein have recognized a potential issue with the above approach. As an example, in situations when both port injectors and direct injectors are operated at the same time, fuel flow from the injectors may outstrip the output of the direct injection fuel pump. This issue may be exacerbated when fuel injectors are operating at a higher fuel flow rate. Herein, pressure in the port injector fuel rail may decrease significantly leading to reduced atomization which may cause a reduction in engine power and an increase in emissions.
The inventors herein have recognized the above-mentioned issues and identified an approach to at least partly address the above issues. In one example approach, a method for an engine may comprise delivering pressurized fuel to a port injector fuel rail from each of a compression chamber of a direct injection fuel pump and a step chamber of the direct injection fuel pump. Thus, the port injector fuel rail may be sufficiently pressurized even during higher fuel flow rates.
For example, a port fuel direct injection (PFDI) engine may receive fuel via both port injection and direct injection. As such, port injectors in the engine may receive fuel from a port injector fuel rail while direct injectors may be fueled via a direct injector fuel rail. A direct injection fuel pump in a fuel system of the PFDI engine pressurizes fuel received from a lower pressure pump and delivers this pressurized fuel to each of the direct injector fuel rail and the port injector fuel rail. Specifically, the direct injector fuel rail may receive fuel from a compression chamber of the direct injection fuel pump while the port injector fuel rail is fluidically coupled to each of the compression chamber of the direct injection fuel pump and a step chamber of the direct injection fuel pump. Thus, pressurized fuel may be delivered to the port injector fuel rail from the compression chamber during a compression stroke in the direct injection fuel pump as long as a spill valve at an inlet to the compression chamber of the direct injection fuel pump remains open (e.g., in a pass-through state). Further, the port injector fuel rail may receive pressurized fuel from the step chamber of the direct injection fuel pump during a suction stroke in the direct injection fuel pump.
In this way, the port injector fuel rail may receive pressurized fuel during a substantial portion of a pump stroke of the direct injection fuel pump. By enabling a relatively constant fuel supply to the port injector fuel rail, a pressure in the port injector fuel rail may be maintained to higher than an output pressure of the lift pump. Thus, port injected fuel may be atomized allowing the PFDI engine to achieve a higher power output. Overall, engine performance may be enhanced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.